This invention relates generally to milling machines, and more particularly, to high-speed CNC milling machines of a type equipped with a position controlled rotary table for holding work pieces and with a motorized cutting tool spindle.
A conventional vertical milling machine is equipped with a horizontal table for holding a work-piece, and a power-rotated cutter for machining the work-piece. The table and the cutting tool of a typical three-axis machine are adapted for relative longitudinal movement along a horizontal X axis, relative lateral movement along a horizontal Y axis, and relative vertical movement along a Z axis. The cutting tool in such machines is typically positioned in a spindle in a vertical position, and in certain machines in a horizontal position or in an adapter for selecting either the vertical or horizontal position. In certain high-performance 4 axis machines, the cutting tool is located in a motorized spindle adapted for pivoting about a horizontal axis A, and in 5 axis machines, for rotation about a vertical axis C1.
A conventional vertical turret lathe is equipped with a horizontal table mounted for continuous rotation of the work-piece about a vertical axis C2, and a non-rotating cutting tool typically positioned in a horizontal position, or in a fixture adapted for pivoting to a fixed position about horizontal axis A. The table and cutting tool are typically adapted for relative positioning along the X and Z axes for positioning of the work piece on the table and machining of the rotating work-piece.
Numerous variations of milling machines and turret lathes are known in the art, as well as several machines that have attempted to merge the benefits of these two types of machines. One prior type of machine includes an adapter permitting removal of the turret lathe horizontal tool holder and installation of a milling vertical tool holding spindle to effect conversion from turret lathe operation to milling operation. Another prior type of machine provides for a turret lathe and a milling station in close proximity in the same machine to reduce transfer time between the two stations. Yet another type of vertical milling machine has been provided with a table mounted for rotation about a vertical axis and for swiveling about a horizontal axis. Other prior milling machines have simply been equipped with a rotary table for milling, rather than turning, cylindrical surfaces.
However, these as well as other prior machines have failed to achieve an effective combination of the machining capabilities of milling machines and turret lathes, coupled with the necessary quick response times, such that the resultant machine is suitable for precision, high-speed CNC milling operations as well as general turning purposes of a conventional turret lathe. Moreover, there is an ever-present need for improved machining apparatus and methods that permit high-speed milling of certain parts which previously could only be manufactured by other less efficient methods, such improved methods and apparatus reducing total manufacturing time, increasing machining accuracy, and/or providing for parts of a desired strength at a reduced weight.
A general aim of the present invention is to provide a new and improved method of high-speed CNC milling capable of machining certain parts which prior milling methods were incapable of machining efficiently, the parts having thus been previously manufactured by other methods.
Briefly, a milling machine according to the invention includes a rotary workpiece-holding table; a dual-mode table drive unit which, in one mode, is adapted for variable speed biodirectional operation with relatively high acceleration and deceleration rates and with relatively small position backlash; a single or dual axis controllable motorized cutting tool spindle releasably mounted for vertical and radial movement with respect to the table; and a control system adapted to achieve a high degree of tool and table position and speed accuracy, the control system comprising a CNC controller, table and tool axes associated sensors to provide the controller with table and tool position and speed feedback signals. For use as a conventional turret lathe, the motorized spindle is replaced with a conventional turret lathe tool holder and the table is rotated utilizing the second table drive mode.
In one embodiment of the present invention, a method of manufacturing a domed-shaped part comprises the steps of providing a domed-shaped blank having an outer surface proximate a desired shape and size, and machining the outer surface to conform the outer surface to the desired shape and size. Preferably, the step of machining the outer surface comprises the steps of positioning the domed-shaped blank on a table of a milling machine having a pivotable cutting tool, sweeping the cutting tool through an arc defined by a profile of the desired shape of the outer surface, and incrementally rotating the domed-shaped blank. This is repeated until an entirety of the outer surface has been machined to conform to the desired shape and size.
The method of the present invention may be utilized to manufacture a variety of different domed-shaped parts. In an embodiment wherein the desired shape is a smooth dome, the step of sweeping comprises sweeping the cutting tool through a constant arc at a distance relative to the dome-shaped blank to form a smooth dome of uniform wall thickness. For domes having reinforcing bands positioned about the outer surface, the step of sweeping comprises sweeping the cutting tool through an arc at a variable distance relative to the dome-shaped blank to form a dome with the reinforcing bands. When a flange at a base of the dome-shaped part is desired, the step of sweeping includes varying the distance relative to the dome-shaped blank in a step fashion to form the flange.
In one embodiment the step of providing a domed-shaped blank comprises the step of forming a metal sheet over a domed-shaped fixture. In an alternate embodiment, the method includes the step of machining an inner surface of the domed-shaped blank to form an isogrid structure.
In an alternate embodiment of the method of the present invention, the method of manufacturing a domed-shaped part comprises the steps of forming a flat metal sheet over a domed-shaped fixture to form a domed-shaped blank having an inner surface conforming to a size and shape of the domed-shaped fixture and having an outer surface proximate a desired shape and size of the domed-shaped part. After this step, the method provides for machining the outer surface of the domed-shaped blank to conform the outer surface to the desired shape and size of the domed-shaped part, and machining the inner surface of the domed-shaped blank to conform the inner surface to the desired shape and size of the domed-shaped part.
In one embodiment of this method, the step of machining the outer surface comprises the steps of positioning the domed-shaped blank on a table of a milling machine having a cutting tool, sweeping the cutting tool through an arc defined by a profile of the desired shape of the outer surface, and incrementally rotating the domed-shaped blank. This is repeated until an entirety of the outer surface has been machined to conform to the desired shape and size of the domed-shaped part. In a further embodiment, the step of sweeping comprises sweeping the cutting tool through the arc at a first position to machine the outer surface to a first wall thickness to form areas of thin-walled dome structure, and at a second position to machine the outer surface to a second wall thickness to form reinforcing bands separated by the areas of thin-walled dome structure. In yet another embodiment, the step of machining the inner surface comprises the step of machining an isogrid structure.